Crestal oscillator and mounting



Aug. 7, 1945. K. G; M LEAN CRYSTAL OSCILLATOR AND MOUNTING Filed April 30, 1942 2 Sheets-Sheet l Aug. 7, 1945. K. G. MacLEAN CRYSTAL OSCILLATOR AND MOUNTING Filed April 30, 1942 2 Sheets-Sheet 2 INVENTOR KENNETH G. MACLE/l/V BY g ATTORNEY Patented Aug. 7, 1945 2,381,173 CBZSTAL OSCILLATOR AND MOUNTING Kenneth G. MacLean,

of Delaware River-head, N. to Radio Corporation of America,

Y., assignor a corporation Application April 30, 1942, Serial No. 441,191

8 Claims.

This invention relates to new and useful crystal oscillator circuits and mounting means which are particularly adapted to radio transmitters.

An object of this invention is to provide novel put and output circuits being tuned to the same frequency.

A feature of this invention resides in the dual use of crystal holder electrodes, so that they will parent application contains the claims directed to the oscillator circuit whereas a divisional application, Serial No. 473,669, filed January 27, 1943, contains the claims directed to the crystal holder and mounting means. The divisional application has now matured into U. S. Patent #2370979.

The several features of this invention are described in more detail in the accompanying specification and with the aid of the accompanying drawings, in which Fig. 1 is a circuit'diagram of a crystal controlled oscillator employing features of my invention.

Fig. 2 is a bridge circuit diagram of Fig. 1.

Fig. 3 is a modified arrangement of the oscillator circuit, shown in Fig. 1.

Mg. 4 is a bridge circuit diagram oscillator, shown in Fig. 3.

Fig. 5 is a still further modification of Fig. l, in which the oscillator is shown employing a-tube of the triode Fig. 6 is a bridge circuit diagram of Fig. 5.

Fig. 7 is a plan view of the crystal holder employed in this invention.

Fig. 8 is a sectional view of Fig. '7.

Fig. 9 is a plan view of a modified crystal holder.

Fig. 10 is a sectional view of Fig. 9.

Fig. 11 is a plan view' of a crystal holder which is particularly adapted for circuit of Fig. 5.

12 is a sectional view of Fig. 11.

Referring now in detail to the crystal controlled oscillator of Fig. 1 of the drawings, the quartz piezo-electric crystal ids provided with electrodes l, 2 and 3. As shown, crystal 5 rests upon a comthe modified mom or lower grounded electrode 4. Tube i. to

use in the oscillator which the crystal is connected, has the usual control grid electrode 8A, plate 63, screen grid 60 and cathode 6D. The internal shielding of the tube is such that the plate to grid capacity is negligible. The input grid 6A is connected to a tuned circuit 1 located within a completely shielded casing 7A. Tuned circuit 1 comprises variable condenser 1B and inductance 1C. The plate 63 is connected to a second tuned circuit 8, located within a shielded container 8A. Circuit 3 comprises variable condenser 83 and inductance 8C. Electrodes l and 2 are connected to points of opposite polarity and are in shunt with a po tion of inductance 8C. Tuned circuits 1 and 8 are designed to resonate-at the crystal resonant frequency, or at some integral harmonic frequency of the crystal 5. 9 is a screen grid by-pass condenser. M and H are grid and plate by-pass condensers respectively. A suitable grid bias re-- sistor i2 is connected in shunt with condenser ill. The screen grid 60 is connected to a suitable D. C. source 03, and the plate 63 is connected with the positive side of a source of D. C. potential H the negative side of which is connected to ground.

In the operation of the circuit shown in Fig. l, oscillations take place only at the crystal frequency, or at an integral harmonic thereof, due to the isolation of tuned circuits 1 and 8, shielded containers 1A and 8A, and the shielding within the tube. Capacity coupling from the crystal electrodes l and 3 is neutralized by a like capacity coupling of the opposite phase from electrodes 2 and 3, which is more clearly shown by the schematic radio frequency bridge circuit diagram of Fig. 2 wherein the electrode surfaces are indi-' cated as a balanced capacitive arm on the left hand side and a balanced inductive arm on the right hand side. The inductive arm includes inductance BC with variable condenser 83 connected in parallel therewith. To the left of the capacitive arm are connected inductance 1C and variable condenser 'lB. The voltage operation is as follows: The electrodes I and 2 receive voltages of equal magnitude but opposite phase. Therefore, the net voltage induced in electrode 3 by the capacities formed by the crystal holder is zero. (This does not mean that 3 is at ground potential but that the capacity feedback has been balanced out.) The voltages on I and 2 also cause distortion of quartz 5 thereby causing a voltage to appear across the quartz under electrode 3 by means of the well known piezoelectric effect. Electrode litherefore now has the potential of the quartz applied to it. This provides voltage to grid 8A of proper phase to cause oscillations to be sustained. The object of the bridge circuit is thus obtained, i. e., the feedback is obtained only by virtue of the feedback through the quartz whereas feedback through the crystal holder electrode capacities is neutralized.

It will be noted by this arrangement that the only feedback irom plate SE to grid on is due to the presence of the quartz crystal in the circuit. A momentary variation 01' plate current, such as would occur when applying plate voltage, will place a voltage on electrodes 2 and 3. This applied voltage causes distortion of the crystal 5, and consequently, as a result, voltage is induced on electrode 3 and tube grid 8A. The phase of this voltage which electrode 3 receives is oi the correct phase for sustaining the desired oscillations.

The modification shown by Figs. 3 and 4 is somewhat similar to that of Figs. 1 and 2, except that an inductive coupled circuit is provided to avoid direct coupling. The inductive coupled coils of circuit 15 are located within a shielded container IA which has also contained therein a. variable condenser 13 and is connected in parallel with the primary coil 15A and grid 6A. The cathode ID is connected directly to ground. A midpoint tap on coil 15A is connected to ground for radio frequency through condenser In. A resistance I2 is connected in shunt with condenser ll. The plate 63 is connected to coil 8C which also has a tap H, a variable condenser 813 connected in shunt with coil 80, both of which are located within a shielded container 8A. A source of D. C. potential It has its positive terminal connected to coil 80. Fig. 3 also shows push-pull neutralization from the grid circuit as compared with pushpul1 neutralization from the plate circuit in Figs. 1 and 2. A blocking condenser i8 is provided to keep the high D. C. voltage from the crystal holder electrodes. The tap II on coil 80 is provided for adjusting the feed-back for optimum excitation of the quartz crystal 5. The schematic radio frequency bridge circuit shown by Fig. 4 shows the grid 6A connected to the variable condenser 1B and coil ISA having a midpoint tap which is connected to ground. A secondary coil I513 has a midpoint tap connected to ground. The coil I53 forms the inductance arm at the left hand side of the bridge. The right hand side of the bridge in cludes capacities formed by electrodes 1 and 3 and 2 and 3, the'electrode 3 being connected to inductance I! by the tap l1.

The further modification shown by Figs. 5 and 6 is for use in a triode type of tube. In this arrangement the plate grid capacity or the triode is also neutralized by suitably proportioning the active capacitive area of electrodes 22 and 23. The circuit is substantially similar to that or the above mentioned circuits shown by Figs. 1 and 2, except that coil IC is provided with two taps I8 and It. Likewise, coil 10 has a coupling coil 2|] connected at the lower portion thereoi. Electrodes 22 and 23 are substituted for electrodes 2 and I, and are preferably in the shape of angular members to give increased capacity by means or the increased area. The schematic circuit shown by Fig. 6 includes the variable tuning condenser 13 inductance 1C, which connects to input grid 8A. Plate 613 is connected to the inductance coil 8C which forms the right hand ductance 8C. The left hand capacitive arm of the bridge is formed by electrodes 1 and 23 and 22 and 23. The capacities to ground are formed by electrodes 3 and 4 and I and 4; also by electrodes 22 and I. In this circuit arrangement there is a small capacity between the plate SB and grid 5A as indicated by the dotted lines. It should be noted that this circuit 01 Figs. 5 and 6 gives as good results as that of Fig, 1, since the plate to grid capacity is neutralized.

The crystal holder shown by Figs. '1 and 8 in-- clude a lower mounting member 25, which is preferably made of insulation material having the necessary requisite insulating qualities as is obtained in such materials as Isolantite, or any suitable ceramic material. The electrodes I, 2 and 3 are located above crystal 5 by means of two insulating rods 26 and '21, which are provided with slots 28 and 29 for locating the elec trodes at a suitable height above crystal 5 to give the desired gap, or air space.

The crystal holder shown in Figs. 9 and i0 is substantially similar to that shown in Figs. 7 and 8, except that one of the electrodes 12 is triangular in shape, illustrating that the electrodesneed not have a symmetrical arrangement.

Figs. 11 and 12 show a modified holder, in which the electrodes 22 and 23 are angular in shape to give thedcsired increased capacity between electrodes. The above mentioned circuits and crystal holder arrangements may also be.

used with push-pull arranged tubes if a holder having four upper electrodes is used and connected, so that the electrodes effectively neutralize capacitive couplings through the crystal. By way of further explanation in connection with the oscillator of Fig. 1, the crystal 5 is provided with a ground electrode i, and three upper electrodes l, 2 and 3. The voltage impressed on electrode I may be adjusted so as to excite the crystal 5 or, in other words, this voltage may be considered feed-back voltage for the production of oscillations imder control of the crystal. When the crystal oscillates an exciting voltage is picked up by means of electrode 3 and impressed upon the grid of tube 8. Undesirable feed-back capacity through l-3 may be neutralized by means of the other crystal electrode capacity 2-4,

In Fig. 5, the feed-back electrode may be considered electrode I, and the grid exciting electrode to be 23. Crystal electrode 22 is provided to balance out or neutralize straight capacity effects, it being noted that electrodes 22 and 23 are provided with upstanding marginal edges which serve to augment the natural capacity between :22 and 23.

What is claimed is:

1. An oscillation generator comprising a vacuum tube having input and output circuits. a piezo-electric crystal having a plurality of electrodes, circuits coupling two of the electrodes arm of a bridge and is connected to ground at the midpoint of coil 8C. Variable condenser 83 of said crystal to input electrodes of said tube. another pair of said crystal electrodes coupled to the output circuit or said tube and means ior appb'ing a neutralizing voltage to still another .pair of electrodes of said crystal to compensate for undesired capacity coupling between said ingut and output circuits, or through the vacuum u e. Y

2. An oscillation generator comprising a tube having an input circuit and an output circuit, a

piezo-electric crystal having a multiplicity ot electrodes, means for feeding voltage from said output circuit to one of said crystal electrodes.

means for feeding voltage from another electrode of said crystal to said input circuit and means for feeding voltage to a third electrode of 7 said piezo-electric crystal, such as to neutralize input circuit and means for feeding voltage to a third electrode of said piezo-electric crystal, such as to neutralize any capacity coupling between said tuned input and output circuits.

4. An oscillation generator comprising a tube having an input circuit and an output circuit, a piezo-electric crystal having a lower grounded electrode and three upper electrodes, means for feeding voltage from said output circuit to one of said upper crystal electrodes, means for feeding voltage from another upper electrode of said crystal to said input circuit and means for feeding voltage to a third upper electrode of said piezoelectric crystal, such as to neutralize any capacity coupling between said input and output circuits.

5. A crystal oscillator circuit comprising a first tuned circuit, a second tuned circuit, an electron discharge device having anode, grid and cathode electrodes, said first tuned circuit being connected to the grid of said electron discharge device, the anode of said electron discharge device being connected to the second tuned circuit, a-

piezo-electric crystal circuit having a plurality of electrodes, one of said electrodes being connected to the grid circuit of said electron discharge device, means for applying an exciting voltage to another electrode of said crystal, and means for applying a neutralizing voltage to still another of said crystal electrodes from said second tuned circuit.

6. A crystal oscillator circuit comprising a first high frequency circuit, a second high frequency circuit, an electron discharge device having grid, anode, screen grid and cathode electrodes, one of said high frequency circuits being connected to the grid of said electron discharge device, the

' anode of said electron discharge device being electron discharge device connected to the other high frequency circuit, a piezo-electric crystal circuit having a plurality of electrodes, oneof said electrodesbeing connected to the grid of said electron discharge device, means for applying a neutralizing voltage to one of the other electrodes of said crystal and means for applying an exciting voltage to still another of said crystal electrodes.

7. A crystal oscillator circuit comprising a first tuned circuit, a second tuned circuit, each of said tuned circuits located within separate shielded containers, an electron discharge device having grid, anode, screen grid and cathode electrodes, said first tuned circuit being connected to the grid of said electron discharge device, the anode of said electron discharge device being connected to the second tuned circuit, means .for producing points of opposite instantaneous polarity in said anode tuned circuit, a piezo-electric crystal circuit having a plurality of electrodes, one of said electrodes being connected to the grid circuit of said electron discharge device, and a pair of electrodes being connected to said points of opposite instantaneous polarity in' the anode circuit of said discharge device, one of said pair of electrodes applying an exciting voltage to said crystal and the other a neutralizing voltage thereto.

8. A crystal oscillator circuit comprising a first tuned circuit, a second tuned circuit, each of said tuned circuits located within separate shielded containers, an electron discharge device having grid, anode, screen grid and cathode electrodes, said first tuned circuit being connected to the grid of said electron discharge device, means for producing points of opposite instantaneous polarity in said grid tuned circuit, the anode of said being connected to the second tuned circuit, a piezo-electricprystal circuit having a plurality of electrodes, one of said electrodes being connected to the anode circuit of-said electron discharge device, and a pair of electrodes being coupled to said points of opposite instantaneous polarity in the grid circuit of said discharge device, one of said pair of electrodes applying an exciting voltage to said grid and the other a neutralizing voltage to said crystal.-

KENNETH G. MACLEAN. 

